The characteristics of long endurance solar powered UAV airborne power and energy storage system is studied and analyzed, and a general design method and process are proposed based on energy balance relation and aerodynamic parameters. The relation formula of energy storage battery (second power supply) weight Qb, solar cell area Ss with the parameters such as weight Qj, flying velocity v, lift-drag ratio k, motor efficiency ηm, propeller efficiency ηB and airborne equipment electric power Pb is derived. On this basis, through a study of the hybrid energy storage with the gravitational potential energy, the relation formula of storage battery weight ratio is derived. This design method is effective through the calculation process and comparison, and the method can provide a reference for the general design method of the long endurance solar power UAV.